2 PROCEEDINGS OF THE NATIONAL MUSEUM vol. u9 



of fluid from tissue by sublimation at low temperatures had been 

 accomplished by Dr. Richard Altman of Leipzig (Glick, 1949, p. 4). 



Only in recent years, with the advent of modern refrigeration and 

 vacuum techniques and equipment that is widely available, has the 

 process become practical for commercial or professional purposes. 

 The process of freeze-drying, now greatly refined, is used currently 

 for food processing and for the preservation of pharmaceuticals, 

 human bone, tissue, and blood plasma. 



The freeze-drying techniques utilized at the Smithsonian Institu- 

 tion for the preservation of biological specimens began in the late 

 1950's (Hower, 1962). There is now a well-established freeze-dry 

 program to preserve many types of natiu-al history specimens for 

 exhibit. Ciu-rent exhibits include freeze-dried rodents, reptiles, 

 crustaceans, insects, and fishes. 



Reflecting on events of past years that led to work on the freeze-dry 

 process, I wish to express my gratitude to Dr. H. T. Meryman of the 

 Biophysics Division of the Navy Medical Research Institute, who 

 pioneered many of the techniques and has made himself always 

 available for consultation. 



Special thanks also are extended to James C. Nyce, who contributed 

 invaluable aid in the preparation of this paper, to Mrs. Constance 

 Minkin, for her writing contributions, and to John Hackmaster, who 

 prepared the illustrations. 



Principles of the Freeze-dry Concept 



Freeze-drying consists bascially of dehydrating tissue while it is 

 frozen. Whereas some tissue dried from a nonfrozen state becomes 

 shrunken and consequently^ distorted in the process, tissue dried from 

 a frozen state virtually retains its original appearance; thus, the process 

 is not only valuable in preserving the quality of food but also in 

 maintaining the appearance of museiun specimens. An additional 

 advantage is that the dehydrated tissue is not subject to decay. 



Compared to other preservation methods, the shrinkage and dis- 

 tortion of freeze-dried museum specimens is minimal, but there is some 

 distortion in certain types of animals, particularly some fishes. In 

 most cases, however, the distortion is negligible or correctable. Fm-ry 

 or feathery specimens and those with exoskeletons appear completely 

 natural when freeze-dried, provided they have been properly prepared. 

 Such preparation includes the positioning of the specimen before 

 dehydration, the actual dehydration, installation of artificial eyes, 

 and the painting of mucous membranes or exoskeletons (mucous 

 membranes become white after dehydration and crustaceans lose their 

 coloration) . 



